Messages in this thread | | | Date | Mon, 17 Aug 2009 11:55:29 +0900 | From | KAMEZAWA Hiroyuki <> | Subject | Re: [PATCH] swap: send callback when swap slot is freed |
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On Wed, 12 Aug 2009 20:07:43 +0530 Nitin Gupta <ngupta@vflare.org> wrote:
> Currently, we have "swap discard" mechanism which sends a discard bio request > when we find a free cluster during scan_swap_map(). This callback can come a > long time after swap slots are actually freed. > > This delay in callback is a great problem when (compressed) RAM [1] is used > as a swap device. So, this change adds a callback which is called as > soon as a swap slot becomes free. For above mentioned case of swapping > over compressed RAM device, this is very useful since we can immediately > free memory allocated for this swap page. > > This callback does not replace swap discard support. It is called with > swap_lock held, so it is meant to trigger action that finishes quickly. > However, swap discard is an I/O request and can be used for taking longer > actions. > > Links: > [1] http://code.google.com/p/compcache/ >
Hmm, do you really need notify at *every* swap free ? No batching is necessary ?
Thanks, -Kame
> Signed-off-by: Nitin Gupta <ngupta@vflare.org> > --- > > include/linux/swap.h | 5 +++++ > mm/swapfile.c | 16 ++++++++++++++++ > 2 files changed, 21 insertions(+), 0 deletions(-) > > diff --git a/include/linux/swap.h b/include/linux/swap.h > index 7c15334..4cbe3c4 100644 > --- a/include/linux/swap.h > +++ b/include/linux/swap.h > @@ -8,6 +8,7 @@ > #include <linux/memcontrol.h> > #include <linux/sched.h> > #include <linux/node.h> > +#include <linux/blkdev.h> > > #include <asm/atomic.h> > #include <asm/page.h> > @@ -20,6 +21,8 @@ struct bio; > #define SWAP_FLAG_PRIO_MASK 0x7fff > #define SWAP_FLAG_PRIO_SHIFT 0 > > +typedef void (swap_free_notify_fn) (struct block_device *, unsigned long); > + > static inline int current_is_kswapd(void) > { > return current->flags & PF_KSWAPD; > @@ -155,6 +158,7 @@ struct swap_info_struct { > unsigned int max; > unsigned int inuse_pages; > unsigned int old_block_size; > + swap_free_notify_fn *swap_free_notify_fn; > }; > > struct swap_list_t { > @@ -295,6 +299,7 @@ extern sector_t swapdev_block(int, pgoff_t); > extern struct swap_info_struct *get_swap_info_struct(unsigned); > extern int reuse_swap_page(struct page *); > extern int try_to_free_swap(struct page *); > +extern void set_swap_free_notify(unsigned, swap_free_notify_fn *); > struct backing_dev_info; > > /* linux/mm/thrash.c */ > diff --git a/mm/swapfile.c b/mm/swapfile.c > index 8ffdc0d..aa95fc7 100644 > --- a/mm/swapfile.c > +++ b/mm/swapfile.c > @@ -552,6 +552,20 @@ out: > return NULL; > } > > +/* > + * Sets callback for event when swap_map[offset] == 0 > + * i.e. page at this swap offset is no longer used. > + */ > +void set_swap_free_notify(unsigned type, swap_free_notify_fn *notify_fn) > +{ > + struct swap_info_struct *sis; > + sis = get_swap_info_struct(type); > + BUG_ON(!sis); > + sis->swap_free_notify_fn = notify_fn; > + return; > +} > +EXPORT_SYMBOL(set_swap_free_notify); > + > static int swap_entry_free(struct swap_info_struct *p, > swp_entry_t ent, int cache) > { > @@ -583,6 +597,8 @@ static int swap_entry_free(struct swap_info_struct *p, > swap_list.next = p - swap_info; > nr_swap_pages++; > p->inuse_pages--; > + if (p->swap_free_notify_fn) > + p->swap_free_notify_fn(p->bdev, offset); > } > if (!swap_count(count)) > mem_cgroup_uncharge_swap(ent); > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ >
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